1. Field of the Invention
This invention relates in general to deposition equipment of the type used for chemical vapor deposition of materials on substrates, and more particularly to a rotatable substrate supporting mechanism with temperature sensing device for use in the deposition chambers of such equipment.
2. Discussion of the Related Art
In the electronics art, it has long been a practice to employ chemical vapor deposition equipment for depositing various materials, on substrates at high temperatures as part of the process of manufacturing semi-conductor devices. Basically, chemical vapor deposition equipment includes a reaction chamber which is heated to a desired reaction temperature and is configured for the controlled flow of the material carrier gas therethrough. A base, which is commonly referred to in the art as a "susceptor", is located in the reaction chamber for supporting the substrates upon which the material is to be deposited by the well known chemical vapor deposition process.
Prior art susceptors are typically of two basic types with the first being a single planar surface for use in a horizontal attitude and the second being an upstanding barrel shaped multi-surface structure. In either case, these susceptors are configured to support a multiplicity of relatively small substrates, i.e., in the neighborhood of 2 to 5 inches in diameter, for simultaneously depositing materials on the multiplicity of substrates. While simultaneous deposition of materials on a multiplicity of substrates is desirable from a manufacturing standpoint, it has some drawbacks from a quality standpoint.
The first problem associated with multi-substrate processing relates to the carrier gas which contains the atoms of the deposition materials. As the gas, which may be referred to as a reactant gas, flows over the surfaces of the substrate and the susceptor, deposition of the materials results in changes in the concentration of the deposition materials in the carrier gas. Consequently, as the reactant gas flows across or over the length of these relatively large susceptors, across each individual substrate and across a multiplicity of such substrates, different rates of growth of the deposited layer of material have been found. A second problem is that of temperature control which is critical at the elevated temperatures needed for proper deposition. It is difficult, if not impossible, to control the temperature within the critical tolerances at all the desired locations within the relatively large reaction chambers. This results in different deposition layer thicknesses from one substrate to another, and can even produce varying thickness within the individual substrates. Still another problem is contamination which can result from various factors such as the handling techniques used to load and unload the substrates, the introduction of the carrier gas into the reaction chamber, and indeed from the reaction chamber itself. The carrier gas not only deposits the deposition material on the substrate, but also deposition takes place on the walls of the reaction chamber. In the relatively large reaction chambers required for multi-substrate processing, the unwanted deposits on the walls of the reaction chambers can be inadvertently incorporated into the growing layers being deposited on the substrates.
These problems and drawbacks, as well as other factors, all contribute to significant problems as the semi-conductor devices and the uses to which they are put become more sophisticated. As a result, many changes and improvements have been made in the equipment that is used to simultaneously process a multiplicity of substrates. For example, some equipment manufacturers are now using automated loading and off-loading devices to eliminate, or at least substantially reduce contamination resulting from human handling. Further, the second type of susceptor discussed above, i.e. the upstanding barrel shaped structure, is being rotated in some instances about its vertical axis to rotate the multiplicity of substrates about that same axis within the reaction chamber. Such barrel rotation is being done for averaging purposes, that is, temperature averaging and reactant gas flow averaging. Obviously these and other things which are being done to improve the simultaneous multi-substrate processing techniques have helped. However, there are practical limits which many feel will ultimately make the simultaneous multi-substrate processing techniques unacceptable or at least undesirable. One of the limitations is that of the equipment being adaptable for handling larger diameter substrates. The economics of larger diameter substrates are causing many manufactures of semi-conductor devices to use larger substrates. However, increasing the size of the substrate is causing some problems with regard to temperature differentials across the substrate, decreasing concentrations of the deposition material as it is carried across the substrate, and the like.
Therefore, steps are being taken now by some equipment manufacturers to make suitable single substrate processing equipment which is significantly simpler in so far as controlling the various factors involved in chemical vapor deposition. Single substrate chemical vapor deposition equipment becomes inherently more desirable than multi-substrate equipment as the manufacturers of semi-conductor devices change to larger substrates, i.e. 5 to 8 inches in diameter or even larger. One important consideration is the cost at risk when processing one substrate as opposed to the simultaneous multi-substrate processing. That is, if something goes wrong, the monetary loss is far less with one substrate that it is with a plurality of substrates. THe susceptors being used in single substrate processing equipment consist essentially of some sort of platform, or base, for supporting the substrate and contribute nothing further to the chemical vapor deposition equipment.
Therefore, a need exists for a new and improved susceptor for use in single substrate chemical vapor deposition equipment which enhances the process and thereby helps in eliminating, or at least reducing, the problems and shortcomings of the prior art.